EPR Study of Ammonium Nitrate Doped with Copper(II) Ions

• Authors: W. Wojtowicz , A. Więckowski
• Languages of publication: EN

Abstracts

EN

This work is devoted to a study of the structural changes in a single crystal of ammonium nitrate, NH_4NO_3, doped with copper(II) cations by electron paramagnetic resonance. Ammonium nitrate crystallizes at atmospheric pressure in several polymorphic forms, phase VII → V → IV → III → II → I → melt, with transition temperatures of 103 K, 255 K, 305 K, 357 K, 398 K, and 443 K, respectively. The aim of our work was to study the temperature phase transition V → IV at about 255 K using electron paramagnetic resonance technique. The electron paramagnetic resonance spectra were performed using an X-band spectrometer with microwave frequency of 9.4 GHz and magnetic modulation of 100 kHz in the temperature range of 153-296 K. For a single crystal the angular dependence of the copper(II) electron paramagnetic resonance spectra was measured at 293 K and 168 K. The anisotropic behaviour measured at 293 K points to the existence of one kind of two equivalent copper(II) complexes with inverse g and A tensors. A second pair of equivalent complexes also with inverse g and A tensors was observed. The minimal values of g-factors correspond to the maximum values of A. The angular dependence taken at 168 K shows the existence of two types of non-equivalent copper complexes which differ in comparison with the complexes observed at room temperature. The temperature dependence of the intensities of hyperfine structure lines for all copper(II) complexes observed shows a phase transition V → IV occurring in the temperature range of 237-246 K with a hysteresis. One of the hyperfine structure lines of a copper(II) complex measured at low temperatures shows a superhyperfine structure with line intensities 1:2:3:2:1 originating from the interaction of the copper ^{63,65}Cu (I=3/2) nucleus with two ^{14}N (I = 1) nuclei of two ammonia, NH_3, ligand molecules.

Keywords

EN

61.50.Ks; 76.30.Fc

Discipline

• 76.30.Fc: Iron group (3d) ions and impurities (Ti-Cu)
• 61.50.Ks: Crystallographic aspects of phase transformations; pressure effects(see also 81.30.Hd in materials science)

• Journal: Acta Physica Polonica A
• Year: 2005
• Volume: 108
• Issue: 2
• Pages: 395-401

Dates

published

2005-08

received

2005-04-24

Contributors

author

W. Wojtowicz

• Institute of Physics, University of Zielona Góra, Prof. Z. Szafrana 4a, 65-516 Zielona Góra, Poland

author

A. Więckowski

• Institute of Physics, University of Zielona Góra, Prof. Z. Szafrana 4a, 65-516 Zielona Góra, Poland

References

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Identifiers

DOI

10.12693/APhysPolA.108.395